1. Field of the Invention
The present invention relates to a substrate for an electro-optical device having a light reflecting layer with concavo-convex portions formed on the surface thereof, a method of manufacturing the substrate for the electro-optical device, an electro-optical device using the substrate for the electro-optical device, an electronic apparatus using the electro-optical device, and a mask for forming a base layer having concavo-convex portions on the surface thereof.
2. Description of the Related Art
Electro-optical devices such as liquid crystal devices are widely used for electronic apparatuses such as cellular phones and portable information terminals. For example, the electro-optical devices are used as display portions for visually displaying various information segments related to the electronic apparatuses.
The electro-optical device comprises, for example, a substrate for an electro-optical device having a reflecting layer and an electro-optical material layer surface-contacting with the reflecting layer such as a liquid crystal layer. The reflecting layer reflects external light such as sunlight and indoor light, thereby supplying the external light to the liquid crystal layer, etc.
In this way, in the case where the external light is reflected by the reflecting layer, when the surface of the reflecting layer is a smooth plane, the background of images such as characters, numbers, and figures displayed outside are mirror-shaped. Therefore, it is difficult to recognize the entire display surface. In order to solve the problem, a technique of forming a plurality of concavo-convex portions, that is, peaks and valleys (concave portions and convex portions (non-concave portions), respectively) on the surface of the reflecting layer and of scattering reflected light has been proposed.
In this way, in order to form the concavo-convex portions on the surface of the reflecting layer, it has been conventionally proposed that a resin layer is formed on a substrate, thereby forming the concave portions or the convex portions with the irregular arrangement in a planar direction on the surface of the resin layer; and thereafter, the reflecting layer is formed on the resin layer, thereby to obtain the substrate provided with the reflecting layer having the irregular surface.
For example, a mask (a photo-mask) 106 illustrated in FIGS. 30A and 30B is used for manufacturing the conventional substrate. When the substrate, illustrated in FIG. 30C, which has a resin layer (a base layer) 102 that is formed on a substrate 101 and concave portions 103 are formed on the surface of the resin layer 102, is manufactured, the mask 106 is formed by disposing a light-shielding layer 108 that consists of holes 104 corresponding to the concave portions 103 and light-shielding portions 109 corresponding to the convex portions on a light transmitting substrate 107.
A layer formed of a photosensitive resin material is exposed through the mask 106. Furthermore, the exposed layer formed of the resin material is developed. As a result, the concave portions 103 are formed on the surface of the resin layer 102. That is, the concavo-convex portions are formed. Furthermore, when a reflecting layer 118 is formed on the resin layer 102, it is possible to form the concavo-convex portions corresponding to the concavo-convex portions of the resin layer 102 on the surface of the reflecting layer 118.
In the light-shielding layer 108 of the conventional mask 106, the positions of the holes 104 corresponding to the light-shielding portions 109 are not specifically determined. Therefore, some holes in the outermost circumferential region among a plurality of holes 104 intersect with an edge of the light-shielding portions 109, that is, an edge 108a of the light-shielding layer 108.
When the conventional mask 106 is used, some parts of the concave portions 103 are formed at an edge 102a of the resin layer 102 on the substrate 101 so as to correspond to the holes 104 which are arranged to intersect with an edge 108a of the light-shielding layer 108, resulting in the edge of the resin layer 102 being made thin in thickness. There is a fear that the thin edge is peeled from the substrate 101 during the development treatment. The peeled pieces of the substrate are again attached onto the substrate 101 or the resin layer 102 after the development treatment and as a result, there is defectiveness in the substrate due to foreign matters. When the pieces are peeled from or attached again onto the resin layer 102, the pattern of the reflecting layer on the pieces 102 becomes uneven. This causes the reflection property of the reflecting layer to become uneven; and when it displays by using the reflecting light, there is a fear that it displays unevenly.
Furthermore, a so called transflective liquid crystal device commonly has a transflective layer for transmitting light and reflecting external light between a liquid crystal layer and a back light unit. A feature of the transflective layer is known as being constructed to transmit light through an aperture and scatter external light by a concavo-convex reflecting surface (a light reflecting portion). Herein, the scattering property is given to the transflective layer in order to prevent the external light from being specularly reflected at the transflective layer and to prevent background or indoor light reflected on the screen from being recognized by an observer, as described above.
As a technique of manufacturing such a transflective layer, one has been proposed to use molding materials such as a photosensitive resin. Specifically, as illustrated in FIGS. 31 and 32, an aperture 512 for transmitting light is provided on a substrate 500 such as glass. A resin layer (a base layer) 510 is formed on the substrate 500 by using a photosensitive resin, the resin layer having a surface provided with concavo-convex portions. Thereafter, a material of light reflectivity, such as Aluminum (Al) is formed only on the concavo-convex portions of the resin layer 510. As a result, a reflecting layer 520 of a shape which corresponds to the shape of the concavo-convex portions of the resin layer 510 is formed. When the resin layer 510 has a light transmitting property, even if the aperture 512 is not formed on the resin layer 510, it is possible to realize a light transmitting display. However, in order to reduce optical loss, it is preferable to form the aperture 512 on the resin layer 510.
The resin layer 510 having the aperture 512 is manufactured, for example, as follows. First, the substrate 500 is coated with positive photosensitive resin; and the photosensitive resin is exposed by a mask 550 which is illustrated in FIG. 33. A light transmitting portion 552 substantially centered in the mask 550 is used for forming the aperture 512 of the resin layer 510. The minute light transmitting portions 554, randomly arranged at the periphery of the light transmitting portion 552, are used for forming a surface provided with the concavo-convex portions on the resin layer 510. When the development treatment is performed after exposing the photosensitive resin by the mask 550, the aperture 512 and the resin layer 510, which are illustrated in FIG. 31, having a surface provided with the concavo-convex portions are formed.
However, in the mask 550, the light transmitting portions 554 for the concavo-convex portions are arranged at an edge of light transmitting portion 552 for the aperture 512 to be close to each other. As illustrated in an enlarged view in FIG. 33, some of the light transmitting portions 554 transmit light at the state ranged along the light transmitting portion 552. Therefore, the sidewall surface 510e of the aperture 512 in the resin layer 510 is wrinkled as illustrated in the plan view of FIG. 31.
However, when the photosensitive material is exposed so that the sidewall surface 510e is wrinkled, there is a probability that resin pieces are peeled from the sidewall surface 510e in the development step. As a result, the resin pieces, which are mixed with a developer, are again attached onto the resin layer. Therefore, this causes a liquid crystal panel to deteriorate in the quality thereof or become defective.